Image display apparatuses, which are represented by liquid crystal display apparatuses and equipped with light sources, and light modulation elements for modulating the intensity of the light emitted from each light source, are now widely used. In the image display apparatuses with the light modulation elements, the contrast of images may well be degraded, because of leakage of light from the light modulation elements, especially when black is displayed. The leakage of light will occur because the light modulation elements do not have ideal modulation characteristics. Further, in these image display apparatuses, the light source luminance is kept constant between different images. Accordingly, it is difficult to realize such highly dynamic range display as in a cathode ray tube (CRT), in which when the average luminance of an input image is high, the display luminance is reduced to suppress glare, and when the average luminance of an input image is low, the display luminance is increased, thereby realizing so-called “sparkling.”
To suppress reduction of contrast in a liquid crystal display apparatus, JP-A 2005-309338 (KOKAI), for example, has proposed a method of providing luminance variable light sources in a plurality of areas on the screen, and executing both the modulation of the luminances of the light sources in accordance with an input image, and the signal level transform of each pixel of the input image.
Further, to enable a liquid crystal display apparatus to perform an operation equivalent to so-called automatic brightness limiter (ABL) control that is executed to realize highly dynamic range display on a CRT, JP-A 2004-350179 (KOKAI), for example, has proposed a method of calculating the average picture level (APL) of an input image, reducing the brightness of a light source if the APL is high, and increasing the brightness if the APL is low.
In both the above-mentioned techniques, such highly dynamic range display as in a CRT is realized by controlling the luminances of the light sources in accordance with the APL of the input image. However, when the process of calculating the APL of the input image is realized by a circuit, if the input image is formed of a large number of pixels like a high definition television (HDTV) image, the scale of the circuit is inevitably extremely increased. Further, when the luminances of the light sources are controlled in accordance with the APL of the input image, it is difficult to control the luminances while limiting the consumption of power, since correlation does not necessarily exist between the APL and the consumption power of the light sources.